The present invention, in some embodiments thereof, relates to biomaterials and, more particularly, but not exclusively, to novel alginate-based compositions, processes of preparing same and therapeutic uses thereof.
Alginate is an anionic polysaccharide derived from brown algae. Alginate is a linear block co-polymer of (1-4)-linked β-D-mannuronic acid (M) and α-L-guluronic acid (G). The monomers can appear in homopolymeric blocks of consecutive G-residues (G-blocks), consecutive M-residues (M-blocks), or alternating M- and G-residues (MG-blocks).
Sodium alginate is soluble in water, and, in the presence of divalent cations, such as calcium ions, alginate forms a hydrogel. In nature, alginate exists in both the soluble form and as a hydrogel. The hydrogel protects brown algae from stress caused by the hydrostatic pressure of water and by waves.
The ratio of mannuronic acid to guluronic acid (M/G) in alginate differs according to the type of algae, and according to environmental conditions. The G residues in alginate have a particularly high affinity to calcium ions. Consequently, the amount of G and length of G-sequences influences the extent of alginate crosslinking and the mechanical properties of the formed hydrogel.
In addition to diversity in M/G ratio, alginate may vary in molecular weight. In nature, alginate usually has a molecular weight in a range of 100-200 kDa. Using different treatment protocols, such as heat and γ-radiation, the molecular weight of alginate can be reduced. Alginates with molecular weights of approximately 50 kDa are commercially available.
International Patent Application PCT/IL97/00191 (published as WO 97/44070) describes implantable polysaccharide (e.g. alginate) sponges for use as a matrix, substrate or scaffold for the cultivation of mammalian cells in vitro prior to their implantation to replace damaged or removed tissue.
International Patent Application PCT/IL2004/000371 (published as WO 2004/098669) describes injectable cross-linked alginate, which forms a hydrogel in vivo, for use in the repair of cardiac tissue damage and ablation of cardiac arrhythmias, when locally applied onto the cardiac tissue.
International Patent Application PCT/IL2008/001552 (published as WO 2009/069131) describes treatment of hepatic disorders via administration of cross-linked or non-cross-linked alginate biomaterial. Local administration to the liver of alginate in solid, hydrogel or liquid form is described, as well as systemic administration by injection of alginate in liquid form.
Landa, N. et al. [Circulation 117:1388-1396 (2008)] describes calcium-crosslinked alginate in an injectable low-viscosity solution, which can undergo phase to transition into a hydrogel after injection. Injection of the alginate solution into a cardiac infarct was reported to prevent adverse cardiac remodeling and dysfunction.
Low-viscosity sodium alginate has been reported to reduce colonic damage and levels of the cytokines IL-6, TNF-α and the eicosanoids LTB4 and PGE2 in a rat model of acute ulcerative colitis induced by intracolonic administration of acetic acid [Mirshafiey et al., Scand J Immunol, 61:316-321 (2005)].
Orally administered calcium alginate (403 kDa) has been reported to reduce liver damage caused by ingestion of CCl4 for one week in mice [Khotimchenko & Khotimchenko, Mar Drugs 2:108-122 (2004)].
Tsur-Gang et al. [Biomaterials 30:189-195 (2009)] describes modification of alginate with the adhesion peptide RGD in order to cause alginate to better interdigitate with the host. RGD-modified alginate is also described in International Patent Application PCT/IL2004/000371 (published as WO 2009/069131).
Liver disease represents a worldwide health problem in humans, which can be managed pharmacologically in only a few cases. Development of new drugs depends primarily on the availability of suitable animal models. The pathophysiology of liver disease includes complex phenomena such as interrelationships on humoral basis, the highly sophisticated morphological organization of the organ itself, and the integrity of metabolic and immunologic pathways and their regulation in the individual cell types of the liver.
The liver is responsible for the synthesis of serum proteins; intermediary metabolism of amino acids, lipids, and carbohydrates; and detoxification of foreign compounds. These functions are usually seriously hampered in the various animal models of liver diseases.
Partial hepatectomy in humans is often needed and well tolerated in the setting of primary of secondary liver tumors [Geller et al. J Gastrointest Surg 10:63-68 (2006)]. Nevertheless, there are cases in which extended partial hepatectomy is warranted due to large hepatic mass and pose a high risk for fulminant hepatic failure [Kubota et al. Hepatology 26:1176-81 (1997)]. To avoid a need for liver transplantation, innovative therapies such as portal vein embolization and staged liver resections have been both used, but have been shown to be associated with considerable morbidity and mortality [Madoff et al. J Vasc Intery Radiol 16:779-790 (2005); Earle et al. J Am Coll Surg 203:436-446 (2006)].
Autoimmune hepatitis is commonly treated by immune suppression, using steroids and immune-modulators for long periods of time (e.g., 3 years). This treatment has significant potential side effects.
Liver damage induced by hepatitis C virus (HCV) is immune-mediated, as HCV is a non-cytopathic virus.
More than 900 drugs have been implicated in causing liver injury [Friedman et al. (2003), Current Diagnosis & Treatment in Gastroenterology, New York: Lang Medical Books/McGraw-Hill. pp. 664-679]. Hepatotoxicity is the most common reason for a drug to be withdrawn from the market, and also accounts for a substantial number of compound failures during drug development. Drug-induced liver injury (DILI) is responsible for 5% of all hospital admissions and 50% of all acute liver failures. Liver function tests are routinely used to monitor subjects taking any of a variety of drugs (e.g., methotrexate, carbamazepine).
Paracetamol (acetaminophen; APAP) intoxication, which may be intentional or unintentional, is one of the major causes of death from drug overdose and may lead to acute liver failure, sometimes irreversibly. Paracetamol-induced liver toxicity is the most prevalent cause of acute liver failure in the Western world. Currently, an accepted treatment is N-acetylcysteine administration, which has several drawbacks, mainly due to its limited therapeutic window.
Knowledge of the mechanisms of paracetamol hepatotoxicity derives to a large extent from studies performed in mice treated with paracetamol. In mice, covalent binding of APAP metabolites to liver proteins begins within 15 minutes of the overdose, concurrently with the beginning of glutathione depletion, and peaks within 1-2 hours. This is followed by other pathogenetic events such as disturbance of intracellular calcium homeostasis, oxidative and nitrosative stress, massive hepatic congestion, and activation of the innate immunity including natural-killer and natural-killer cells with T-cell receptors, macrophages and neutrophils. Oncotic necrosis is the main mode of hepatocyte cell death.
Alcoholic liver disease is the major cause of liver disease in Western countries. Chronic consumption of alcohol results in the secretion of pro-inflammatory cytokines (TNF-α, IL-6 and IL-8), oxidative stress, lipid peroxidation, and acetaldehyde toxicity. These factors cause inflammation, apoptosis and eventually fibrosis of liver cells.
Additional art includes International Patent Application Publication WO 95/19743; International Patent Application Publication WO 98/12228; International Patent Application Publication WO 2004/082594; German Patent Application Publication DE 19723155 A1; Ichi et al. [J Nutr Sci Vitaminol 53:53-56 (2007)]; Seifert & Phillips [Biotechnol Prog 13:562-568 (1997)]; Balakrishnan & Jayakrishnan [Biomaterials 26:3941-3951 (2005)]; Maruyama et al. [J Surg Res 58:29-294 (1995)]; and Dvir-Ginzberg et al. [Tissue Engineering 9:757-766 (2003)].